Technical Abstract:
The sugarcane borer, Diatraea saccharalis (F.), has been the dominant stemborer of sugar cane in the United States. However, in 1980, the Mexican rice borer, Eoreuma loftini (Dyar), became established in the Lower Rio Grande Valley of Texas and has since supplanted the sugarcane borer as the dominant insect pest of that industry. The Mexican rice borer has since expanded its range and now threatens the sugar cane industry in Louisiana. Although dissimilar in several aspects of their biology, there are sufficient similarities that it seems likely that a high degree of cross-resistance for the two species exists in sugar cane. While researching a molecular approach to breeding for stemborer resistance, we were presented with the opportunity to evaluate sugar cane varieties from both Louisiana and Texas in the presence of both stemborer species.
In 2004 we planted 80 sugar cane varieties in a randomized complete block design with four replications. Individual plots were 6 m in length. Random 10-stalk samples were collected from each plot in 2005 for damage evaluation. Damage was measured as percent damaged internodes. Mexican rice borer was the predominate borer species and responsible for 23% (±0.62) bored internodes verses 7% (±0.33) bored internodes for the sugarcane borer. Texas varieties averaged 22% (±0.73) damage internodes by the Mexican rice borer while Louisiana varieties averaged 25% (±1.09). For the sugarcane borer, damaged internodes averaged 8% (±0.46) for Texas varieties and 5% (±0.42) for Louisiana varieties. We found strong statistical evidence for cross-resistance among the Louisiana varieties, but no evidence among the Texas varieties. We have ratooned the study with plans to collect another year of data in 2006. Meanwhile, molecular markers are being applied to these genotypes in an attempt to tag major resistance genes involved in stemborer resistance.